Oxygen ion conducting ceramic material and use thereof

ABSTRACT

It is an object of the present invention to provide a ceramic member with excellent balance between oxygen ion conductivity and endurance (resistance to cracking and the like), an oxygen ion permeation module and a chemical reactor such as an oxygen separator, using such a ceramic member. The ceramic member with oxygen ion conductivity in accordance with the present invention has a perovskite-type crystal structure and a composition represented by the general formula (Ln 1-x M x )(Ti 1-y Fe y )O 3  (where Ln represents at least one element selected from lanthanoids, and M represents at least one element selected from the group containing Sr, Ca, and Ba, 0&lt;x&lt;1, 0.4≦y&lt;1, x+y≧1). The oxygen ion permeation module composed by employing such a ceramic member can be used as a structural component of an oxygen separator, an oxidation reactor (for example, a reactor for partial oxidation of hydrocarbons), and the like.

FIELD OF TECHNOLOGY

The present invention relates to a ceramic member with oxygen ionconductivity for causing selective permeation of oxygen ions. Further,the present invention also relates to an oxygen ion permeation moduleemploying the ceramic member. Moreover, the present invention alsorelates to a chemical reactor such as an oxygen separator or anoxidation reactor (for example, a reactor for partial oxidation ofhydrocarbons), which is comprised of said oxygen ion permeation module.

BACKGROUND TECHNOLOGY

Ceramics (oxygen ion conductors) having the property of causingselective permeation of oxygen ions at a high temperature (for example,500° C. or higher) are known. Ceramic members formed from such oxygenion conductors can be used with the object of separating oxygen from anoxygen-containing gas mixture. For example, an oxygen separation methodusing zirconium oxide as an oxygen ion conductor is known. In arepresentative modification of such a separation method, as shown inFIG. 11, external electrodes (not shown in the Figure) are pasted onboth surfaces of a membranous ceramic member (oxygen permeable membrane)composed of zirconium oxide, and those electrodes are short circuitedwith an external circuit 116. This ceramic member 110 is disposed sothat the partial pressure of oxygen at one surface side 110 b of themembranous ceramic member 110 is lower than the partial pressure ofoxygen on the other surface side 110 a thereof. With such aconfiguration, on one surface 110 a of the ceramic member 110, oxygenmolecules accept electrons and become oxygen ions, and those oxygen ionsdiffuse (are conducted) in zirconium oxide and reach the other surface110 b where they discharge the electrons and become oxygen molecules.The discharged electrons are returned to the other surface 110 a via theexternal circuit 116. As a result, oxygen is continuously separated fromthe gas, which is in contact with one surface 110 a of the ceramicmember 110. Technology of this type was disclosed in Japanese Patent No.3,173,724 (Japanese Patent Application Laid-open No.H10-180031) andJapanese Patent Application Laid-open No.H9-299749.

On the other hand, some oxygen ion conductors demonstrate electronconductivity (the meaning of this term also includes hole conductivity),together with oxygen ion conductivity. Such oxygen ion conductors arealso sometimes called electron—oxygen ion mixed conductors (hereafterreferred to as “mixed conductors”). In the membranous ceramic memberscomposed of such mixed conductors, as shown in FIG. 12, the ceramicmember 120 itself has electron conductivity, and it is possible to causea continuous permeation of oxygen ions from one surface 120 a to theother surface 120 b, without using external electrodes or an externalcircuit for short-circuiting the two surfaces. Technology of this typewas openly disclosed in Japanese Patent Applications Laid-open Nos.2001-106532, 2001-93325, 2000-154060, H 11-335164, H1 1-335165,H10-114520, and S56-92103, Japanese Patent No. 2,533,832 (JapanesePatent Application Laid-open No. H6-198149), Japanese Patent No.2,813,596 (Japanese Patent Application Laid-open No. H6-219861),Japanese Patent No. 2,966,340 (Japanese Patent Application Laid-open No.H8-276112), Japanese Patent No. 2,966,341 (Japanese Patent ApplicationLaid-open No. H9-235121), Japanese Patent No. 2,993639 (Japanese PatentApplication Laid-open No. H11-253769), U.S. Pat. Nos. 5,306,411 and5,356,728, Japanese Patent Application Laid-open Nos. 2001-269555,2002-12472, and 2002-97083.

Examples of representative oxygen ion conductors include perovskite-typemixed conductors of the LaSrCoO₃ type. Such conductors have a crystalstructure in which part of La in a perovskite-type structure based onLaCoO₃ is substituted with Sr. Furthermore, perovskite-type mixedconductors of the LaSrCoFeO₃ type with a crystal structure, in whichpart of Co is replaced with a transition metal element such as Fe, havealso been suggested. In conductors of such composition, the oxygen ionconductivity tends to increase, as the rate of substitution of La withSr increases. However, in compositions with a high Sr substitution rate,when a membranous ceramic member composed of such a conductor is formed(fired), cracks easily appear in the ceramic member during use thereof(for example, when used as an oxygen permeable membrane). In particular,when such a conductor is exposed to a reducing atmosphere, the conductoris reduced. As a result, the crystal structure of the conductor changesand cracks can easily originate therein. The cracked ceramic member canno longer demonstrate its inherent performance (oxygen separationability and the like). Thus, the ceramic member composed of a conductorwith such a composition has poor endurance.

Examples of other representative oxygen ion conductors include mixedconductors having a perovskite-type structure of the LnGaO₃ type (Ln isa lanthanoid). For example, a mixed conductor was suggested that had acrystal structure in which part of Ln in a perovskite-type structurebased on LnGaO₃ was substituted with an alkaline earth metal elementsuch as Sr, and part of Ga was substituted with Fe. Such mixedconductors of the LnGaO₃ type have high resistance to reduction (theyare not easily reduced even when exposed to a reducing atmosphere,thereby maintaining their crystal structure). However, ceramic membersformed from mixed conductors of the LnGaO₃ type are relatively expensivedue to the high cost of starting materials. Accordingly, there is ademand for ceramic members that have good endurance (resistance toreduction) and can be formed from an oxygen ion conductor that can bemanufactured at a low cost.

On the other hand, the ceramic members formed from the aforesaid oxygenion conductors can also be used in reactors for oxidation, for examplefor partial oxidation of hydrocarbons. For example, the ceramic memberis formed into a membrane (this term includes also thin layers), onesurface thereof is brought into contact with a gas containing oxygen,and the other surface is brought into contact with a gas containing ahydrocarbon (methane or the like). As a result, the hydrocarbon that isbrought into contact with one surface of the ceramic member can beoxidized with oxygen ions that are supplied through the ceramic memberfrom the other surface of the membranous ceramic member. In order toincrease the efficiency of this oxidation reaction, a catalyst (Ni orthe like) for enhancing the oxidation reaction can be applied to thefirst surface of the ceramic member. However, when a ceramic memberformed from the conventional oxygen ion conductor (for example, of theLaSrCoO₃ type, the LnGaO₃ type, or the like) is used for partialoxidation of the hydrocarbons, some of the supplied hydrocarbonsdecompose on the first side of the ceramic member, and the catalysteasily degrades due to catalyst poisoning by the carbon thatprecipitates as a result of such decomposition.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a ceramic memberwith an excellent balance of oxygen ion conductivity and endurance (forexample, resistance to cracking). It is another object of the presentinvention to provide a ceramic member that inhibits carbon precipitationwhen hydrocarbons or other compounds containing carbon atoms areoxidized using the ceramic member. It is yet another object of thepresent invention to provide an oxygen ion permeation module using sucha ceramic member. It is still another object of the present invention toprovide an oxygen separation method using such a ceramic member and anoxygen separator employed in such a method. Furthermore, still anotherobject of the present invention is to provide a method for oxidizinggases of a variety of types, which are the objects of oxidation, usingsuch a ceramic member and an oxygen reactor to be used in such a method(for example, a method for partial oxidation of hydrocarbons and areactor for partial oxidation of hydrocarbons used in such a method).

The inventors have found that the above-described problems can beresolved with a ceramic member that is formed from a ceramic having acrystal structure in which part of Ln in a perovskite-type structurebased on LnBO₃ (Ln=lanthanoid) is replaced with a specific alkalineearth metal, and its B sites are occupied with Ti or Fe.

One of the ceramic members provided by the present invention is formedfrom a ceramic having a perovskite-type crystal structure and acomposition represented by the general formula:(Ln_(1-x)M_(x))(Ti_(1-y)Fe_(y))O₃   (A)In the general formula (A), Ln represents at least one element(preferably La) selected from lanthanoids. M represents at least oneelement selected from the group containing Sr, Ca, and Ba. Furthermore,x is typically within a range of 0<x<1, and y is within a range of0.4≦y<1. Further, x+y≧1. Such a ceramic member is suitable forapplications in which selective permeation of oxygen ions is induced.

Here, in the aforesaid general formula (A), the number of oxygen atomsis shown to be 3, but actually the number of oxygen atoms is 3 or less(typically less than 3). However, accurate representation is difficultbecause the number of oxygen atoms varies depending on the type of atoms(here, M and Fe) used for partial substitution of the perovskitestructure, the degree of substitution, and other conditions.Accordingly, in the present specification, in the general formularepresenting the perovskite-type materials, the number of oxygen atomsis shown to be 3 for the sake of convenience. However, thisrepresentation should not be construed as limiting the technologicalscope of the invention disclosed herein. Therefore, the number of oxygenatoms can also be written as 3-z (for example, the aforesaid generalformula (A) can be represented as(Ln_(1-x)M_(x))(Ti_(1-y)Fe_(y))O_(3-z)). Here z is typically a positivenumber (0<z<1) that does not exceed 1.

Such a ceramic member is formed from a ceramic with a structure, inwhich the B sites in the perovskite-type crystal structure, representedby LnBO₃, are occupied by Ti and Fe. The specific combination of Ti withFe increases resistance to reduction (resistance to the occurrence ofcracking when the material is exposed to a reducing atmosphere).Furthermore, when the ceramic member is used for oxidation ofhydrocarbons or other carbon-containing compounds, precipitation ofcarbon on the ceramic member surface is suppressed. Therefore, when anoxidation-enhancing catalyst (Ni-based catalyst and the like) is appliedto the surface of the ceramic member, degradation of the catalyst isdiminished. Moreover, the inventors were the first to discover that theeffect of preventing the occurrence of cracking and/or suppressing theprecipitation of carbon can be obtained by occupying the B sites in theaforesaid crystal structure with a specific combination of elements,that is, with Ti and Fe.

In the preferred embodiment of the ceramic member in accordance with thepresent invention, this ceramic member is formed from a ceramic(sintered body) having a perovskite-type crystal structure and acomposition that can be represented by the general formula:(Ln_(1-x)Sr_(x))(Ti_(1-y)Fe_(y))O₃   (1)In the general formula (1), Ln represents at least one element(preferably La) selected from lanthanoids. Furthermore, x is typicallywithin a range of 0.3≦x≦0.5, and y is within a range of 0.85≦y<1.

In another preferred embodiment of the ceramic member in accordance withthe present invention, this ceramic member is formed from a ceramichaving a perovskite-type crystal structure and a composition that can berepresented by the general formula:(Ln_(1-x)Ba_(x))(ti_(1-y)Fe_(y))O₃   (2)In the general formula (2), Ln represents at least one element(preferably La) selected from lanthanoids. Furthermore, x is typicallywithin a range of 0.4≦x≦0.6, and y is within a range of 0.85≦y<1.

In yet another preferred embodiment of the ceramic member in accordancewith the present invention, this ceramic member is formed from a ceramichaving a perovskite-type crystal structure and a composition that can berepresented by the general formula:(Ln_(1-x)Ca_(x))(Ti_(1-y)Fe_(y))O₃   (3)In the general formula (3), Ln represents at least one element(preferably La) selected from lanthanoids. Furthermore, x is typicallywithin a range of 0.25≦x≦0.45, and y is within a range of 0.85≦y<1.

The ceramic member formed from a ceramic having a compositionrepresented by any of the aforesaid general formulas (1) to (3) candemonstrate especially excellent oxygen ion conductivity.

In yet another preferred embodiment of the ceramic member in accordancewith the present invention, this ceramic member is formed from a ceramichaving a perovskite-type crystal structure and a composition that can berepresented by the general formula:(Ln_(1-x)Sr_(x))(Ti_(1-y)Fe_(y))O₃   (4)In the general formula (4), Ln represents at least one element(preferably La) selected from lanthanoids. Furthermore, x is typicallywithin a range of 0.2≦x≦0.6, and y is within a range of 0.5≦y<1.Further, x+y is within a range of 1≦x+y<1.2.

In yet another preferred embodiment of the ceramic member in accordancewith the present invention, this ceramic member is formed from a ceramichaving a perovskite-type crystal structure and a composition that can berepresented by the general formula:(Ln_(1-x)Ba_(x))(Ti_(1-y)Fe_(y))O₃   (5)In the general formula (5), Ln represents at least one element(preferably La) selected from lanthanoids. Furthermore, x is typicallywithin a range of 0.3≦x≦0.7, and y is within a range of 0.5≦y<1.Further, x+y is within a range of 1 ≦x+y<1.2.

In yet another preferred embodiment of the ceramic member in accordancewith the present invention, this ceramic member is formed from a ceramichaving a perovskite-type crystal structure and a composition that can berepresented by the general formula:(Ln_(1-x)Ca_(x))(Ti_(1-y)Fe_(y))O₃   (6)In the general formula (6), Ln represents at least one element(preferably La) selected from lanthanoids. Furthermore, x is typicallywithin a range of 0.2≦x≦0.55, and y is within a range of 0.5≦y<1.Further, x+y is within a range of 1≦x+y<1.2.

The ceramic member formed from a ceramic having a compositionrepresented by any of the aforesaid general formulas (4) to (6) candemonstrate especially excellent endurance (for example, a highresistance to cracking when exposed to a reducing atmosphere).

Any of the ceramic members provided in accordance with the presentinvention can be formed into a membrane (this term includes thin sheets,tubes, and other layered products). Such a membranous ceramic member canbe composed by applying a catalyst for enhancing the permeation ofoxygen ions to at least one surface of the membrane. Catalystscomprising (La_(x)Sr_(1-x))(M′O₃ (where 0.1≦x<1, and M′ is at least oneselected from Co, Cu, Fe, and Mn) are preferably used as the catalystfor enhancing the permeation of oxygen ions. Ceramic members of suchconfiguration are suitable as structural components of thebelow-described oxygen separators and oxidation reactors for oxidizing avariety of gases, which are the objects of oxidation (for example,reactors for partial oxidation of hydrocarbons).

The present invention provides a laminated oxygen ion conductive part(also called a laminated ceramic part) of a configuration in which amembranous ceramic member is provided on the surface of a porous supportbody (porous support layer). The membranous ceramic member has aperovskite-type crystal structure and a composition that can berepresented by the general formula (Ln_(1-x)M_(x))(Ti_(1-y)Fe_(y))O₃.Here, Ln represents at least one element (typically La) selected fromlanthanoids. M represents at least one element selected from the groupcontaining Sr, Ca, and Ba. Furthermore, typically 0<x<1, 0.4≦y<1, andx+y≧1. In a typical example of the laminated oxygen ion conductive partin accordance with the present invention, the aforesaid membranousceramic member has a composition represented by the aforesaid generalformula (A). In the preferred embodiment of the present invention, theaforesaid membranous ceramic member has a composition represented by anyof the aforesaid general formulas (1)-(3). In another preferredembodiment of the present invention, the aforesaid membranous ceramicmember has a composition represented by any of the aforesaid generalformulas (4)-(6).

For the porous support body constituting such a laminated oxygen ionconductive part, a material is preferably used that possesses stableheat resistance in the temperature range in which such laminated oxygenion conductive parts are used (usually, 300° C. or higher, typically500° C. or higher). For example, ceramic porous bodies having acomposition similar to that of any of the above-described ceramicmembers, or ceramic bodies based on magnesia or zirconia can be used.Furthermore, metallic porous bodies based on a metal material andorganic porous bodies based on resin materials with high heat resistance(for example, polyamides, polyamidoimides, and polybenzimidazole) mayalso be used.

In one preferred embodiment of the laminated oxygen ion conductive partin accordance with the present invention, a membranous ceramic member isformed on part of the surface of such a porous support body. No specificlimitation is placed on the shape of the porous support body and it canbe in the form of a membrane (layer) shaped as a sheet or a tube. Insuch membranous porous support bodies, the membranous ceramic member ispreferably formed on one or both surfaces of the membrane. With such aconfiguration, one surface of the membranous ceramic member ismechanically supported, by the porous support body. Therefore, theendurance of the ceramic member can be further increased. As a result,the endurance of the laminated oxygen ion conductive part can be furtherincreased.

The laminated oxygen ion conductive part can have a configuration inwhich a catalyst for enhancing the permeation of oxygen ions is appliedto the surface of the aforesaid ceramic member and/or to the aforesaidporous support body. Catalysts comprising (La_(x)Sr_(1-x)))M′O₃ (where0.1≦x<1, and M′ is at least one selected from Co, Cu, Fe, and Mn) arepreferably used as the catalyst for enhancing the permeation of oxygenions.

When the ceramic member in accordance with the present invention isformed into a membrane, the preferred thickness of the membranousceramic member is 10 μm to 5 mm, preferably 20 μm to 3 mm, and morepreferably 50 μm to 2 mm. Furthermore, the same thickness is preferredfor the membranous ceramic member formed on the surface of the poroussupport body in the laminated oxygen ion conductive part in accordancewith the present invention. The performance characteristics, such asoxygen ion permeability and endurance, of a ceramic member having amembrane thickness within this range can be balanced at a high level.

An oxygen ion permeation module provided in accordance with the presentinvention comprises:

-   -   a casing,    -   a ceramic member accommodated in the casing,    -   an oxygen source supply chamber for supplying an        oxygen-containing gas from the outside, this chamber being        provided inside the casing so as to face the ceramic member, and    -   an oxidation reaction chamber that is provided inside the casing        so as to face the ceramic member, that is hermetically separated        from the oxygen source supply chamber via the ceramic member,        and that induces an oxidation reaction with the participation of        the oxygen ions that are supplied by permeation through the        ceramic member from said oxygen source supply chamber.

The ceramic member used in the module has a perovskite-type crystalstructure and a composition that can be represented by the generalformula:(Ln_(1-x)M_(x))(Ti_(1-y)Fe_(y))O₃.Here, Ln represents at least one element (typically La) selected fromlanthanoids. M represents at least one element selected from the groupcontaining Sr, Ca, and Ba. Furthermore, typically 0<x<1, 0.4≦y<1, andx+y≧1.

In a typical example of the oxygen ion permeation module in accordancewith the present invention, the aforesaid ceramic member has acomposition represented by the aforesaid general formula (A). In thepreferred embodiment of the present invention, the ceramic member has acomposition represented by any of the aforesaid general formulas(1)-(3). In another preferred embodiment of the present invention, theaforesaid ceramic member has a composition represented by any of theaforesaid general formulas (4)-(6).

Still another preferred embodiment of the oxygen ion permeation modulein accordance with the present invention is a membrane-type oxygen ionpermeation module in which the aforesaid ceramic member is formed as amembrane, and a catalyst for enhancing the permeation of oxygen ions isapplied to at least the surface of the membranous ceramic member that ison the side of the oxygen source supply chamber.

Yet another preferred embodiment of the oxygen ion permeation module inaccordance with the present invention is a membrane-type oxygen ionpermeation module in which the aforesaid ceramic member is formed as amembrane, and a catalyst for enhancing the oxidation reaction is appliedto at least the surface of the membranous ceramic member that is on theside of the oxidation reaction chamber.

Still another preferred example of the oxygen ion permeation module inaccordance with the present invention is a membrane-type oxygen ionpermeation module in which the aforesaid ceramic member is formed as amembrane, a catalyst for enhancing the permeation of oxygen ions isapplied to at least the surface of the membranous ceramic member that ison the side of the oxygen source supply chamber, and a catalyst forenhancing the oxidation reaction is applied to at least the surface ofthe membranous ceramic member that is on the side of the oxidationreaction chamber.

Another oxygen ion permeation module provided in accordance with thepresent invention comprises:

-   -   a casing,    -   a laminated oxygen ion conductive part accommodated in the        casing,    -   an oxygen source supply chamber for supplying an        oxygen-containing gas from the outside, this chamber being        provided inside the casing opposite the laminated oxygen ion        conductive part, and    -   an oxidation reaction chamber that is provided inside the casing        opposite the laminated oxygen ion conductive part, that is        hermetically separated from the oxygen source supply chamber via        the laminated oxygen ion conductive part, and that induces an        oxidation reaction with the participation of the oxygen ions        that are supplied by permeation through the ceramic member from        said oxygen source supply chamber. Any of the above-described        laminated oxygen ion conductive parts in accordance with the        present invention can be used as the laminated oxygen ion        conductive part constituting the module.

Such an oxygen ion permeation module can have a configuration in which acatalyst for enhancing the permeation of oxygen ions is applied to thesurface of the aforesaid ceramic member on the side of the oxygen sourcesupply chamber and/or to the aforesaid porous support body positioned onthe oxygen source supply chamber side of the aforesaid ceramic member.Furthermore, a configuration is possible in which a catalyst forenhancing the oxidation reaction is applied to the surface of theaforesaid ceramic member on the side of the oxidation reaction chamberand/or to the aforesaid porous support body positioned on the oxidationreaction chamber side of the aforesaid ceramic member. The oxygen ionpermeation module may also contain both the catalyst for enhancing thepermeation of oxygen ions and the catalyst for enhancing the oxidation.

No specific limitation is placed on the type of the catalyst forenhancing the permeation of oxygen ions, which is used in any of theoxygen ion permeation modules in accordance with the present invention.Those catalysts for enhancing the permeation of oxygen ions that contain(La_(x)Sr_(1-x))M′O₃, for example, (where 0.1≦x<1, and M′ is at leastone selected from Co, Cu, Fe, and Mn) are preferably used. A catalystfor enhancing the permeation of oxygen ions, in which M′ is Co isespecially preferred. It is also preferred that an Ni-based catalyst beincluded as the catalyst for enhancing the oxidation that is used in anyof the oxygen ion permeation modules in accordance with the presentinvention.

The present invention provides an oxygen separator equipped with such anoxygen ion permeation module, an oxidation reactor (typically a reactorfor partial oxidation of hydrocarbons) for oxidizing the various typesof gases that are the objects of oxidation, and a chemical reactor usedfor various types of chemical reactions, which are accompanied byoxidation reaction.

Thus, the oxygen separator, provided by the present invention, comprisesany of the above-described oxygen ion permeation modules;

-   -   an oxygen source supply means for causing a gas containing        oxygen to flow through to the oxygen source supply chamber of        the module, and bringing the gas into contact with the surface        of the ceramic member on the side of the oxygen source supply        chamber; and    -   an oxidation reaction chamber gas-circulation means for causing        a gas with a partial pressure of oxygen lower than that on the        oxygen source supply chamber side to flow through to the        oxidation reaction chamber of the module, and bringing the gas        into contact with the surface of the ceramic member on the side        of the oxidation reaction chamber and a module thereof.

The ceramic member, provided in such an oxygen separator, candemonstrate both the oxygen ion conductivity and the electronconductivity. Therefore, such an oxygen separator can have aconfiguration in which no external electrodes are used forshort-circuiting the surfaces of the ceramic member on the side of theoxygen source supply chamber and the side of the oxidation reactionchamber. A configuration using the external electrode may also be used.

Such an oxygen separator is advantageously suitable as an apparatus forthe implementation of an oxygen separation method comprising the stepsof:

-   -   causing a gas containing oxygen to flow through to the oxygen        source supply chamber of the oxygen permeation module in        accordance with the present invention, and bringing the gas into        contact with the surface of the aforesaid ceramic member on the        side of the oxygen source supply chamber; and    -   causing a gas with a partial pressure of oxygen lower than that        on the oxygen source supply chamber side to flow through to the        oxidation reaction chamber of the module, and bringing the gas        into contact with the surface of the ceramic member on the side        of the oxidation reaction chamber.

Further, the oxidation reactor (for example, a reactor for partialoxidation of hydrocarbons) provided by the present invention comprisesany of the above-described oxygen ion permeation modules;

-   -   an oxygen source supply means for causing a gas containing        oxygen to flow through to the oxygen source supply chamber of        the module, and bringing the gas into contact with the surface        of the aforesaid ceramic member on the side of the oxygen source        supply chamber; and    -   an oxidation-target gas supply means for supplying a gas,        containing the oxidation-target gas and having a partial        pressure of oxygen lower than that on the oxygen source supply        chamber side, to the oxidation reaction chamber of the module        and bringing the gas into contact with the surface of the        ceramic member on the side of the oxidation reaction chamber.

The ceramic member, provided in such an oxidation reactor, candemonstrate both oxygen ion conductivity and electron conductivity.Therefore, such a reactor can have a configuration in which no externalelectrodes are used for short-circuiting the surfaces of the aforesaidceramic member on the side of the oxygen source supply chamber and theside of the oxidation reaction chamber. A configuration using anexternal electrode may also be used.

Such an oxidation reactor is preferably used as a reactor for thepartial oxidation of hydrocarbons in which a hydrocarbon is supplied asthe aforesaid oxidation-target gas. Such a reactor for the partialoxidation of hydrocarbons is preferably used under conditions such thatthe supply flow rate of the oxygen that is supplied by the aforesaidoxygen source supply means is higher by a factor of two or more than theflow rate of the hydrocarbon supplied by the oxidation reaction chambergas-circulation means. As a result, the hydrocarbon oxidation efficiencycan be increased.

Such an oxidation reactor is advantageously suitable as an apparatus forthe implementation of an oxidation method (for example, a method for thepartial oxidation of hydrocarbons) comprising the steps of:

-   -   supplying a gas containing oxygen to the oxygen source supply        chamber of the oxygen permeation module in accordance with the        present invention, and bringing the gas into contact with the        surface of the aforesaid ceramic member on the side of the        oxygen source supply chamber; and    -   supplying a gas, containing the oxidation-target gas (for        example, a hydrocarbon) and having a partial pressure of oxygen        lower than that on the oxygen source supply chamber side, to the        oxidation reaction chamber of the module and bringing the gas        into contact with the surface of the ceramic member on the side        of the oxidation reaction chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view illustrating a configurationexample of the oxygen ion permeation module in accordance with thepresent invention;

FIG. 2 is a schematic diagram illustrating a general configuration ofthe oxygen separator in accordance with the present invention;

FIG. 3 is a schematic cross-sectional view illustrating the maincomponents in another configuration example of the oxygen ion permeationmodule in accordance with the present invention;

FIG. 4 is a schematic cross-sectional view illustrating the maincomponents in another configuration example of the oxygen ion permeationmodule in accordance with the present invention;

FIG. 5 is a schematic cross-sectional view illustrating the maincomponents in another configuration example of the oxygen ion permeationmodule in accordance with the present invention;

FIG. 6 is a schematic cross-sectional view illustrating the maincomponents in another configuration example of the oxygen ion permeationmodule in accordance with the present invention;

FIG. 7 is a schematic cross-sectional view illustrating the maincomponents in another configuration example of the oxygen ion permeationmodule in accordance with the present invention;

FIG. 8 is a schematic cross-sectional view illustrating the maincomponents in another configuration example of the oxygen ion permeationmodule in accordance with the present invention;

FIG. 9 is a schematic explanatory drawing illustrating the mode in whichoxygen separation is performed with a ceramic member to which an oxygenion permeation-enhancing catalyst is applied;

FIG. 10 is a schematic explanatory drawing illustrating the mode inwhich the partial oxidation reaction of methane is performed with aceramic member to which an oxygen ion permeation-enhancing catalyst andan oxidation-enhancing catalyst are applied;

FIG. 11 is a schematic explanatory drawing illustrating the mode inwhich oxygen separation is performed with a ceramic member composed ofzirconium oxide; and

FIG. 12 is a schematic explanatory drawing illustrating the mode inwhich oxygen separation is performed with a ceramic member composed ofan electron-oxygen ion mixed conductor.

BEST MODE FOR CARRYING OUT THE INVENTION

The preferred embodiments of the present invention will be describedbelow.

First the ceramic member in accordance with the present invention willbe explained. The ceramic member in accordance with the presentinvention is formed from a ceramic having a composition represented bythe general formula:(Ln_(1-x)M_(x))(Ti_(1-y)Fe_(y))O₃.Here, Ln represents at least one element selected from lanthanoids(typically La, Ce, Pr, Nd, and Sm), preferably La. Further, M representsat least one element selected from the group containing Sr, Ca, and Ba,of the alkali earth metal elements.

In the aforesaid general formula, “x” is a value representing the ratioat which the Ln in the perovskite-type structure is substituted with M.The x value can be within a range of 0<x<1 (preferably 0.05≦x≦0.95). Alarge x value is preferred from the standpoint of increasing oxygen ionconductivity. On the other hand, if the x value becomes too large,cracks can sometimes easily appear in the ceramic member.

The preferred range of the x value in accordance with the presentinvention differs depending on the type of M. Thus, when M is Sr, thepreferred range is 0.2≦x≦0.6, and the more preferred range is 0.3≦x≦0.5.When M is Ba, the preferred range is 0.3≦x≦0.7, and the more preferredrange is 0.4≦x≦0.6. When M is Ca, the preferred range is 0.2≦x≦0.55, andthe more preferred range is 0.25≦x≦0.45.

In the aforesaid general formula, “y” is a value representing the ratioat which the Ti in the perovskite-type structure is substituted with Fe.The y value can be, for example, within a range of 0.4≦x<1. Thepreferred range of the y value is 0.5≦x<1, and the more preferred rangeis 0.85≦x<1. If the y value is too small (if the Ti ratio is too high),the oxygen ion conductivity tends to decrease. The use of a ceramicmember in which the y value is within the aforesaid range, can preventthe occurrence of cracking and/or suppress the precipitation of carbon,while maintaining an oxygen ion conductivity suitable for practical use.Furthermore, it is preferred that in the ceramic member in accordancewith the present invention, x and y satisfy the condition x+y≧1. It ispreferred that x and y satisfy the condition 1≦x+y<1.6, and it is morepreferred that they satisfy the condition 1≦x+y<1.2. It is especiallypreferred that x and y satisfy the condition 1≦x+y<1.15.

The ceramic member in accordance with the present invention is formedfrom a ceramic demonstrating at least oxygen ion conductivity.Typically, the ceramic member is formed from a ceramic demonstratingoxygen ion conductivity and electron conductivity. When the ceramicmember is formed from a ceramic demonstrating mainly oxygen ionconductivity, a ceramic member with excellent oxygen ion conductivitycan be obtained.

Further, when the ceramic member is formed to have a membranous shapefrom a ceramic demonstrating electron conductivity in addition to oxygenion conductivity (mixed conductor), oxygen ions can be caused topermeate continuously from one surface of the ceramic member to another,without using an electrode or an external circuit for short-circuitingthe two surfaces of the membranous ceramic member. The ceramic memberthus used preferably has a level of electron conductivity such that theelectric conductivity, σ, at a temperature of 800° C. is log σ=−1.2S/cm² or more (preferably log σ=−0.4 S/cm² or more). Such a level ofelectron conductivity can be achieved, for example, in a ceramic memberthat satisfies the conditions 0<x≦0.65 and 0.85<y<1 in the aforesaidformulas. Furthermore, such a level of electron conductivity is realizedespecially easily when y is within a range of 0.5≦y<1 (more preferably0.85≦y<1) and x is within the aforesaid preferred range corresponding tothe type of M (Sr, Ba, or Ca).

No specific limitation is placed on the shape of the ceramic member. Inthe preferred embodiment of the present invention, the ceramic member isformed to have a membranous shape. Here, the term “membranous” is ageneral term including flat, curved, tubular (open-end tubular shape inwhich both ends are open, and a closed-end tubular shape in which oneend is open), and honeycomb-like shapes. Oxygen ions can be effectivelycaused to permeate from one surface of the membrane to the other surfaceby creating different partial pressures of oxygen on both sides of themembrane. It is preferred that the membrane be dense (for example, therelative density is 95% or more of the theoretic density) andsubstantially gas-impermeable. The thickness of the ceramic member canbe, for example, 0.5 μm to 10 mm, preferably 1 μm to 5 mm, morepreferably 2 μm to 3 mm, and still more preferably 5 μm to 2 mm. Theceramic member of the composition represented by any of the generalformulas (4) to (6) is preferably a membranous ceramic member with athickness of 1 mm or less (typically 5 μm to 1 mm), especiallypreferably a membranous ceramic member with a thickness of 0.5 mm orless (typically 50 μm to 0.5 mm).

The ceramic member in accordance with the present invention can bemanufactured, for example, in the manner described below. Thus, powders(starting material powders) of compounds comprising metal atoms thatwill constitute the ceramic that is to be manufactured are mixed at theprescribed ratio. The mixture is molded and fired in an oxidizingatmosphere (for example, in air) or in an inactive gas atmosphere toobtain a ceramic. Here, powders comprising at least one of the oxidescontaining metal atoms that will constitute a ceramic, or compounds(carbonates, nitrates, sulfates, phosphates, acetates, oxalates,halides, hydroxides, oxyhalides, and the like) that can be convertedinto oxides by heating can be used as the aforesaid starting materialpowder. The starting material powders may also contain compounds(complex metal oxides, complex metal carbonates, and the like)containing metal atoms of no less than two types among the metal atomsthat will constitute a ceramic.

The appropriate firing temperature differs depending on the compositionof the ceramic, but is typically 1200-1800° C. (preferably 1400-1700°C.). Furthermore, the firing process can comprise at least one prefiringstep and a main firing step conducted thereafter. In this case, the mainfiring step is conducted at the aforesaid firing temperature, and theprefiring step is preferably conducted at a firing temperature (forexample, 800-1500° C.) lower than that of the main firing step.

The molding of the starting material powder or the molding of theprefired powder obtained by grinding the prefired product can beconducted by using a conventionally known molding method such asuniaxial compression molding, hydrostatic pressing, extrusion molding,and the like. A conventional binder can be used for such molding.

The ceramic member in accordance with the present invention can alsocontain components other than the ceramic represented by the aforesaidgeneral formula, within a range in which the performance thereof (oxygenconductivity, electron conductivity, cracking prevention ability, carbonprecipitation suppressing ability, and the like) is not degradedsignificantly.

“A catalyst for enhancing the permeation of oxygen ions” can be appliedto the surface of the membranous ceramic member to enhance thepermeation of oxygen ions. A compound comprising a metal of at least onetype selected from the group including Pt, Pd, Ru, Au, Ag, Bi, Ba, V,Mo, Ce, Pr, Co, Rh, and Mn and/or the metal oxides (spinel-type complexoxide, perovskite-type complex oxide, and the like) can be used as thecatalyst for enhancing the permeation of oxygen ions. Furthermore, atleast one of the conventionally known oxygen ion conductors, forexample, an LaSrCoO₃ type, an LaGaO₃ type, an LaCoO₃ type, an LaFeO₃type, an SeFeO₃ type, and stabilized zirconia can also be used. Amongthem, the catalyst for enhancing the permeation of oxygen ions, which ispreferably used, contains CaTiO₃ or a perovskite-type complex oxiderepresented by the formula (La_(x)Sr_(1-x))M′O₃ (where 0≦x≦1 and M′ isat least one selected from Co, Cu, Fe, and Mn). The especially preferredcatalyst contains (La_(x)Sr_(1-x))CoO₃ (where 0.1≦x<1).

The catalyst for enhancing the permeation of oxygen ions, such as(La_(x)Sr_(1-x))CoO₃ is a catalyst (ceramic) which, by itself, hasoxygen ion conductivity. However, when the ceramic member obtained byforming this ceramic ((La_(x)Sr_(1-x))CoO₃) into a membrane is exposedto a reducing atmosphere, cracks easily occur therein. The ceramic, inaccordance with the present invention, can have a configuration in whicha catalyst for enhancing the permeation of oxygen ions, with acomposition of (La_(x)Sr_(1-x))CoO₃ is applied to the membrane formedfrom a ceramic represented by (Ln_(1-x)M_(x))(Ti_(1-x)Fe_(y))O₃. As aresult, it is possible to obtain a ceramic member in which both oxygenion conductivity and cracking prevention ability can be demonstrated ata high level due to the synergistic effect of the cracking preventionability of the ceramic represented by (Ln_(1-x)M_(x))(Ti_(1-y)Fe_(y))O₃and the oxygen ion conductivity of the ceramic having a composition of(La_(x)Sr_(1-x))CoO₃.

Such a catalyst for enhancing the permeation of oxygen ions may beapplied to only one surface of the membranous ceramic member or to bothsurfaces. It is preferred that the catalyst be applied (coated) so as tocover the entire surface on one side or both sides of the ceramicmember, but it may also be applied only to a partial region (forexample, in the form of spots, stripes, a grid, or the like). Nospecific limitation is placed on the method for “applying” the catalystto the surface of the ceramic member. For example, the target catalystcan be applied (coated) by preparing a slurry containing the catalystpowder, coating this slurry on the surface of the ceramic member anddrying it. The applied catalyst powder may be thereafter additionallyfired.

Further, “a catalyst for enhancing the oxidation reaction” can beapplied to the surface of such a membranous ceramic member. Theconventionally known oxidation catalysts and/or dehydrogenationcatalysts such as compounds comprising at least one metal selected fromthe group including Ni, Rh, Ag, Au, Bi, Mn, V, Pt, Pd, Ru, Cu, Zn, Co,Cr, Fe, In-Pr mixtures, and In-Sn mixtures and/or the metal oxides canbe used as the aforesaid catalyst for enhancing the oxidation reaction.Among them, Ni-based catalysts (catalysts composed based on Ni) orRh-based catalysts (that is, catalysts composed based on Rh) arepreferably used.

Such a catalyst for enhancing the oxidation reaction can be applied toone or both surfaces of the membranous ceramic member (to the entiresurface or partial regions thereof), using a method identical to thatused for applying the aforesaid catalyst for enhancing the permeation ofoxygen ions. Furthermore, both the catalyst for enhancing the permeationof oxygen ions and the catalyst for enhancing the oxidation reaction canalso be applied to one surface or both surfaces of the membranousceramic member.

Catalysts for enhancing the permeation of oxygen ions and/or catalystsfor enhancing the oxidation reaction may be disposed in the vicinity ofthe surface of the ceramic member and do not necessarily have to bedirectly applied to the surface of the ceramic member. For example, theaforesaid catalyst(s) may be supported by a porous support body, of thelaminated oxygen ion conductive part, in accordance with the presentinvention. (For example, a catalyst layer is formed on the surface thatis opposite the surface where the membranous ceramic member has beenformed.) Alternatively, the catalytic effect can be used by employing amethod such as filling the oxygen source supply chamber, or theoxidation reaction chamber, with ceramic pellets supporting thosecatalysts.

The oxygen ion permeation module in accordance with the presentinvention will be described below. In the oxygen ion permeation modulein accordance with the present invention, the ceramic member isaccommodated in a casing. Inside the casing, the oxygen source supplychamber and the oxidation reaction chamber are formed so that they arehermetically separated from each other by the ceramic member. The oxygensource supply chamber faces one of the surfaces of the ceramic memberand the oxidation reaction chamber faces the other surface, and the twochambers are hermetically separated from each other by the ceramicmember. The ceramic member is preferably formed to have a membranousshape. A module can be configured such that the above-described oxygenion permeation-enhancing catalyst is applied to at least the surface ofthe membranous ceramic member on the side of the oxygen source supplychamber. There may be one ceramic member or several ceramic membersaccommodated in one module. Furthermore, one or several oxygen sourcesupply chambers and oxidation reaction chambers may be provided in onemodule. The number of the oxygen source supply chambers provided in onemodule may be equal to or different from the number of the oxidationreaction chambers.

Ceramics having a perovskite-type crystal structure and a compositionrepresented by the aforesaid general formulas (1) to (6) can, bythemselves, have the properties of an oxygen ion permeation-enhancingcatalyst. For this reason, the membranous ceramic member, the laminatedoxygen ion conduction part, and the oxygen ion permeation module inaccordance with the present invention, which are constituted, based onsuch ceramics, can demonstrate oxygen ion conductivity sufficient forpractical use, even when the aforesaid oxygen ion permeation-enhancingcatalyst is not used. Therefore, they can be advantageously used asstructural parts of oxygen separators, oxidation reactors, and the like.

In the preferred oxygen ion permeation module used in thebelow-described oxygen separator, a membranous ceramic member isprovided in which an oxygen ion permeation-enhancing catalyst (forexample, (La_(x)Sr_(1-x))CoO₃, where 0.1≦x<1) is applied at least to thesurface of the ceramic member on the side of the oxygen source supplychamber (preferably, both on the surface on the side of the oxygensource supply chamber and on the surface on the side of the oxidationreaction chamber). FIG. 9 is an explanatory drawing illustratingschematically the mode in which oxygen is separated with a ceramicmember 60 to both sides of which the oxygen ion permeation-enhancingcatalyst 61 is applied. On one surface 60 a (the surface on the side ofthe oxygen source supply chamber) of the ceramic member 60, oxygenmolecules accept electrons and become oxygen ions. Those oxygen ionsdiffuse through the ceramic member 60 and reach the other surface 60 b(surface on the side of the oxidation reaction chamber). Here, theoxygen ions discharge the electrons and become oxygen molecules. In thisprocess, the reaction of oxygen ion generation from the oxygen moleculesand/or the reaction of oxygen molecule generation from the oxygen ions,is enhanced by the oxygen ion permeation-enhancing catalyst 61.

In the preferred oxygen ion permeation module used in thebelow-described reactor for partial oxidation of hydrocarbons, amembranous ceramic member is provided in which an oxygen ionpermeation-enhancing catalyst is applied to the surface on the side ofthe oxygen source supply chamber and an oxidation enhancing catalyst(for example, an Ni-based catalyst) is applied to the surface on theside of the oxidation reaction chamber. FIG. 10 is an explanatorydrawing illustrating schematically the mode in which methane ispartially oxidized with such a ceramic member 65. An oxygen ionpermeation-enhancing catalyst 61 is applied to one surface 65 a (thesurface on the side of the oxygen source supply chamber) of the ceramicmember 65, and the oxidation-enhancing catalyst 62 is applied to theother surface 65 b (the surface on the side of the oxidation reactionchamber. On one surface 65 a, oxygen molecules accept electrons andbecome oxygen ions. These oxygen ions diffuse through the ceramic member60 and reach the other surface 65 b. Here, they are brought into contactwith and oxidize methane, producing reaction products such as CO, CO₂,and H₂. In this process, the reaction of oxygen ion generation from theoxygen molecules and/or the partial oxidation reaction of methane withthe oxygen ions is enhanced by the oxygen ion permeation-enhancingcatalyst 61 and the oxidation-enhancing catalyst 62.

The oxygen separator in accordance with the present invention will bedescribed below.

The oxygen separator in accordance with the present invention comprisesa means for causing an oxygen-containing gas to flow through to theoxygen source supply chamber of the above-described oxygen permeationmodule, and bringing the gas into contact with the surface of theaforesaid ceramic member on the side of the oxygen source supplychamber. The gas (an oxygen-containing gas) supplied by this meanstypically contains 10-100 vol. % oxygen. The oxygen-containing gaspreferably used is air. The pressure of the atmosphere inside the oxygensource supply chamber when the aforesaid oxygen separator is used (thepressure of the oxygen-containing gas) may be a normal pressure(atmospheric pressure), or may be an increased or reduced pressure.Typically, it is a normal pressure or an increased pressure, preferably,a normal pressure.

This oxygen separator comprises a means for causing “a gas (the gas ofthe oxidation reaction chamber) with a partial pressure of oxygen lowerthan that on the side of the oxygen source supply chamber” to flowthrough to the oxidation reaction chamber of the oxygen permeationmodule, and bringing it into contact with the surface of the ceramicmember on the side of the oxidation reaction chamber. A gas with anoxygen content lower than that on the side of the oxygen source supplychamber (for example, 0.01 vol. % or less, the gas may also containsubstantially no oxygen) or a gas with a pressure lower than that on theside of the oxygen source supply chamber is preferably used as theoxidation reaction chamber gas. Furthermore, the pressure of theatmosphere (gas that flows through to the oxidation reaction chamber)may be a normal pressure or may be increased or reduced. Typically, itis a normal pressure or a reduced pressure, preferably, a normalpressure.

From the standpoint of increasing the oxygen permeation efficiency inthe oxygen separator, it is preferred that the oxygen separator be used(operated) in a state in which the difference in the partial pressure ofoxygen between the oxygen source supply chamber and the oxidationreaction chamber be large. For example, if the partial pressure ofoxygen on the side of the oxygen source supply chamber is assumed to be1, then the partial pressure of oxygen on the side of the oxidationreaction chamber is preferably not higher than 10⁻², more preferably nothigher than 10⁻³. Furthermore, from the standpoint of decreasing theload (stresses) applied to the ceramic member, it is preferred that thedifference in pressure between the oxygen source supply chamber and theoxidation reaction chamber be small. For example, the pressure ratio ispreferably 2 or less, more preferably 1.2 or less. It is even morepreferred that the pressure in the oxygen source supply chamber be equalto that in the oxidation reaction chamber.

With the oxygen separator in accordance with the present invention, inthe oxidation reaction chamber, oxygen molecules are generated fromoxygen ions that permeated through the ceramic member from the oxygensource supply chamber to the oxidation reaction chamber. The oxygenmolecules are removed together with the oxidation reaction chamber gasfrom the oxidation reaction chamber with the oxidation reaction chambergas circulation means. As a result, oxygen can be separated from theoxygen-containing gas that was supplied to the oxygen source supplychamber. Further, the oxygen separator may be provided with one orseveral oxygen permeation modules.

This oxygen separator is typically used under the following conditions.That is, the temperature of the ceramic member during oxygen separationis preferably 300° C. or higher (typically 300-1500° C.), preferably500° C. or higher (typically 500-1500° C.), more preferably 800° C. orhigher (typically 800-1200° C.). The flow rate of the oxygen-containinggas supplied into the oxygen source supply chamber by the oxygen sourcesupply means (for example, a supply source such as an air cylinder orair compressor and a valve connected thereto) can be, for example,10-5000 mL/min. The flow rate of the oxygen (oxygen supply rate) in theoxygen-containing gas supplied into the oxygen source supply chamber ispreferably within a range of 50-2500 mL/min. Furthermore, the flow rateof the gas supplied into the oxidation reaction chamber by the oxidationreaction chamber gas circulation means can be, for example, 1-500mL/min.

The oxygen separator in accordance with the present invention canseparate oxygen (calculated as oxygen molecules) at a rate of 15μmol/min or more (more preferably 20 μmol/min or more) per unit surfacearea (cm²) of the ceramic member at a temperature of 900° C., forexample.

The oxidation reactor in accordance with the present invention will bedescribed below.

The reactor in accordance with the present invention comprises an oxygensource supply means identical to that of the aforesaid oxygen separator.Further, this reactor also comprises an oxidation-target gas supplymeans that supplies “a gas (an oxidation reaction chamber gas) thatcontains an oxidation-target gas (for example, a hydrocarbon) and has apartial pressure of oxygen lower than that in the oxygen source supplychamber” into the oxidation reaction chamber of the oxygen permeationmodule and brings it into contact with the surface of the ceramic memberon the side of the oxidation reaction chamber.

With the reactor provided in accordance with the present invention, itis possible to conduct “a reaction of partial oxidation ofhydrocarbons”, such as the reaction of generating a synthetic gas (a gascontaining H₂ and CO at a volume ratio of 2:1) from methane, naturalgas, or the like, and the reaction of generating unsaturatedhydrocarbons (olefins and the like) from saturated or unsaturatedhydrocarbons with a low molecular weight (for example, ethane, propane,ethyl benzene, or the like). Further, this oxidation reactor can also beused as a reactor for oxidation reactions of other types in which oxygenions participate. Examples of such oxidation reactions include theoxidation of reducible gases other than hydrocarbons (for example, thegeneration of H₂O by oxidation of hydrogen gas), the substitution ofaromatic compounds, and the like. The composition and flow rate of thegas supplied into the oxidation reaction chamber, the composition of theceramic constituting the ceramic member, the presence and type of theoxidation-enhancing catalyst, the reaction temperature, etc. are setappropriately according to the type of the aforesaid oxidation reaction.The preferred partial pressure of oxygen in the gas (that contains anoxidation-target gas such as a hydrocarbon) to be supplied to theoxidation reaction chamber, and the preferred difference in pressurebetween the oxygen supply source chamber and the oxidation reactionchamber are identical to those described hereinabove with reference tothe oxygen separator. This reactor may comprise one or several oxygenpermeation modules.

Such an oxidation reactor (for example, a reactor for partial oxidationof hydrocarbons) is typically used under the following conditions. Thatis, the preferred temperature of the ceramic member during the oxidationreaction is usually 300° C. or higher (typically 300-1500° C.),preferably 500° C. or higher (typically 500-1500° C.), more preferably800° C. or higher (typically 800-1200° C.). The flow rate of theoxygen-containing gas supplied into the oxygen source supply chamber bythe oxygen source supply means can be, for example, 10-5000 mL/min(preferably 50-2500 mL/min). The flow rate of the oxygen (oxygen supplyrate) in the oxygen-containing gas supplied into the oxygen sourcesupply chamber is preferably within a range of 10-1500 mL/min(preferably 50-1000 mL/min). Furthermore, the flow rate of the gassupplied into the oxidation reaction chamber (gas containing theoxidation-target gas such as a hydrocarbon) by the oxidation-target gassupply means (for example, a cylinder containing the oxidation-targetgas such as a hydrocarbon, and a valve connected thereto) can be, forexample, 1-500 mL/min (preferably 1-250 mL/min, more preferably 5-60mL/min). The flow rate of the oxidation-target gas in the gas suppliedinto the oxidation reaction chamber is preferably within a range of1-500 mL/min (more preferably 1-250 mL/min, even more preferably 1-50mL/min).

When the reactor is a reactor for partial oxidation of hydrocarbons, theflow rate of oxygen supply is preferably no less than 2 times, morepreferably no less than 5 times, even more preferably no less than 10times the flow rate of hydrocarbons (the hydrocarbon flow rate) in thegas supplied by the oxidation-target gas supply means. As a result, thesupplied hydrocarbon can be converted into a partial oxide thereof withgood efficiency. The reactor (for example, a reactor for partialoxidation of hydrocarbons) in accordance with the present invention canbe used for a reaction in which oxygen (calculated as oxygen molecules)is caused to permeate from the oxygen source supply chamber to theoxidation reaction chamber at a rate of 25 μmol/min or more per unitsurface area (cm²) of the ceramic member at a temperature of 1000° C.,for example, and to oxidize (for example, partially oxidize) theoxidation-target gas (for example, a hydrocarbon). In a more preferredembodiment, the reactor can be used for a reaction in which oxygen iscaused to permeate from the oxygen source supply chamber to theoxidation reaction chamber at a rate of 50 μmol/min or more (in an evenmore preferred embodiment, 80 μmol/min or more) per unit surface area,and oxidize the oxidation-target gas.

An embodiment of the oxygen ion permeation module provided in accordancewith the present invention and examples of the devices comprising such amodule will be described below.

FIG. 1 shows an example of an oxygen ion permeation module using aceramic member formed to have a flat shape. This oxygen ion permeationmodule 1 comprises a flat ceramic member 10 and a casing 40 foraccommodating the ceramic member 10. The casing 40 is formed from adense ceramic such as mullite. The casing 40 comprises an oxygen sourcesupply chamber casing 22 positioned on the side of one of the surfacesof the ceramic member 10 and an oxidation reaction chamber casing 32positioned on the side of the other surface of the ceramic member 10.The oxygen source supply chamber casing 22 comprises a closed-endcylindrical outer tube 24, one end of which is hermetically bonded toone of the surfaces 10 a of the ceramic member 10; and a cylindricalinner tube 26 one end of which penetrates through the bottom of theouter tube 24 and is hermetically inserted into the outer tube 24. Athroughhole 25 is formed in the side wall of the outer tube 24. Theoxidation reaction chamber casing 32 similarly comprises a closed-endouter tube 34, one end of which is hermetically bonded to the othersurface 10 b of the ceramic member 10; and a cylindrical inner tube 36,one end of which penetrates through the bottom of the outer tube 34 andis hermetically inserted into the outer tube 34. A throughhole 35 isformed in the side wall of the outer tube 34. The oxygen source supplychamber 20 is separated and formed by the oxygen source supply chambercasing 22 and the ceramic member 10. Further, the oxidation reactionchamber 30 is separated and formed by the oxidation reaction chambercasing 32 and the ceramic member 10.

FIG. 2 schematically illustrates the oxygen separator configured usingthe oxygen ion permeation module shown in FIG. 1. In this oxygenseparator 50, an oxygen source supply means 52 for causing the air toflow to the oxygen source supply chamber 20 and bringing it into contactwith one surface 10 a of the ceramic member 10 is connected to theoxygen source supply chamber 20 of the oxygen ion permeation module 1.The oxygen source supply means 52 is constructed, as shown in FIG. 1, sothat the oxygen-containing gas (in this case, air) is supplied from theother end 26 b of the inner tube 26 into the oxygen source supplychamber 20 and discharged from the throughhole 25 of the outer tube 24.On the other hand, as shown in FIG. 2, an oxidation reaction chamber gascirculation means 54 for causing nitrogen gas to flow into the oxidationreaction chamber 30 and bringing it into contact with the other surface10 b of the ceramic member 10 is connected to the oxidation reactionchamber 30 of the oxygen ion permeation module 1. This oxidationreaction chamber gas circulation means 54, is constructed, as shown inFIG. 1, so that the oxidation reaction chamber gas (in this case,nitrogen) is supplied from the throughhole 35, of the outer tube 34,into the oxidation reaction chamber 30 and discharged from the other end36 b, of the inner tube 36. Further, the oxygen separator 50 shown inFIG. 2 also comprises a heating means (a heater or the like) for heatingthe ceramic member 10 to the desired temperature.

The air and nitrogen are caused by the oxygen source supply means 52 andthe oxidation reaction chamber gas circulation means 54 to flow throughthe oxygen ion permeation module 1, while the ceramic member 10 ismaintained at the prescribed usage temperature (for example, 500° C. orhigher) with the heating means 56. As a result, the oxygen that wascontained in the air supplied to the oxygen source supply chamber 20becomes oxygen ions and permeates through the ceramic member 10. Thoseoxygen ions become oxygen molecules in the oxidation reaction chamber 30and are extracted to the outside. Oxygen separation is thus conducted.

The oxygen ion permeation module 1 shown in FIG. 1 uses one ceramicmember 10 formed to have a flat shape. However, as shown in FIG. 3, anoxygen ion permeation module may also be configured so that a pluralityof flat ceramic members 10 are arranged in a stack and the air(oxygen-containing gas) and nitrogen (oxidation reaction chamber gas)are alternately passed through the channels formed between the adjacentceramic members 10. Furthermore, the oxygen ion permeation module 1shown in FIG. 1 may also have a configuration comprising a stack-typeoxygen ion conductive part 19 provided with a porous support body 11 formechanically supporting the ceramic member 10 on the side of the othersurface 10 b of the ceramic member 10, as shown in FIG. 4. Further, inthe configuration shown in FIG. 4, the porous support body 11 isprovided on the side of the other surface 10 b of the ceramic member 10,but the porous support body 11 may also be provided on the side of thefirst surface 10 a or on both surfaces of the ceramic member 10.Moreover, the support may be provided for the entire surface of theceramic member, as shown in FIG. 4, or it may support only part of thesurface.

FIG. 5 shows an example of the oxygen ion permeation module using theceramic member 12 formed into a tube. This oxygen ion permeation module2 comprises a tubular ceramic member 12 and a casing 42 foraccommodating the ceramic member 12. The casing 42 is formed from adense ceramic such as mullite. The casing 42 has a hollow cylindricalshape and the tubular (open-end tube) ceramic member 12 passes in theaxial direction through both ends of the casing. Two throughholes 43, 44are formed in the side surface of the casing 42. In this oxygen ionpermeation module 2, the oxygen source supply chamber 20 is separatedand formed by the ceramic member 12 itself, inside the tubular ceramicmember 12. Further, a tubular oxidation reaction chamber 30 is separatedand formed by the casing 42 and the ceramic member 12. This oxygen ionpermeation module 2 can be used in the oxygen separator 50 shown in FIG.2 instead of the oxygen ion permeation module 1 shown in FIG. 1.

Further, a single ceramic member 12 formed into a tube (open-end tube)was used in the oxygen ion permeation module 2 shown in FIG. 5, but anoxygen ion permeation module with a structure in which a plurality ofceramic members 12 pass through in the axial direction of the casing 42,as shown in FIG. 6, may also be used. In such an oxygen ion permeationmodule, the inside of each ceramic member 12 is used as the oxygensource supply chamber 20, and the space between the casing 42 and theceramic member 12 is used as the oxidation reaction chamber 30.

Furthermore, while in the oxygen ion permeation module 2 shown in FIG. 5and FIG. 6, a ceramic member 12 having both ends open passes through thecasing 42, a configuration can also be used in which a ceramic memberhaving one end (the distal end) closed (closed-end tubular ceramicmember) 12 can also be provided inside the casing 42, as shown in FIG.7. The number of closed-end tubular ceramic members 12 provided insideone casing 42, may be more then one. An example of the configurationcomprising a single ceramic member 12 is shown in FIG. 7. With such aconfiguration, the number of places where the closed-end ceramic member12 and the casing 42 are sealed can be reduced in comparison with theconfiguration in which the open-end ceramic member 12 passes through thecasing 42. Accordingly, an oxygen ion permeation module 2 with a tightlysealed casing 42 can be obtained. As shown in FIG. 7, an inner tube 13with both ends open may be disposed inside the closed-end tubularceramic member 12. The distal end of the inner tube 13 extends to thevicinity of the distal end of the closed-end ceramic member.Furthermore, a tubular gap is formed between the inner periphery of theclosed-end ceramic member 12 and the outer periphery of the inner tube13. If air is supplied inside the inner tube 13 and then passed throughthe aforesaid gap from the distal end of the inner tube 13, then atleast part of the oxygen contained in the supplied air will be convertedinto oxygen ions and permeates through the closed-end tubular ceramicmember 12. Those oxygen ions become oxygen molecules inside theoxidation reaction chamber 30 and are extracted to the outside.

Further, as shown in FIG. 8, an oxygen permeation module can also beconfigured using a ceramic member 14 formed to have a honeycomb shape.This honeycomb ceramic member 14 has a cylindrical columnar outer shape.A plurality of channels 15 is formed inside the ceramic member so as topass through the ceramic member 14 in the axial direction, thosechannels being separated by partitions 10 a. The channels can begenerally classified into channels 15 a (oxygen source supply chambers)for passing oxygen-containing gas and channels 15 b (oxidation reactionchamber) for passing the oxidation reaction chamber gas. The channels 15a and 15 b are arranged alternately. In the oxygen permeation modulecomprising such ceramic member 14, the oxygen-containing gas and theoxidation reaction chamber gas are passed independently through thosechannels 15 a and 15 b, and such a module can be used as a structuralelement of the oxygen separator 50 as shown in FIG. 2.

Any of the above-described oxygen ion permeation modules, can also beused by reversing the position of the oxygen source supply chamber, andthe position of the oxidation reaction chamber. For example, in theoxygen ion permeation module 2 shown in FIG. 5, the inside of theceramic member 12 may be used as the oxidation reaction chamber 30, andthe space between the ceramic member 12 and the casing 42 may be used asthe oxygen source supply chamber 20. Furthermore, the flow direction ofthe oxygen-containing gas and the oxidation reaction chamber gas is notlimited to that shown in the Figures. For example, in the oxygen ionpermeation module 2 shown in FIG. 5, nitrogen may be supplied from thethroughhole 44 and discharged from the throughhole 42. Moreover, in theabove-described oxygen separator, the outer electrodes and outercircuits for short circuiting the two surfaces of the ceramic memberwere not used, but a device may also be configured in which they areused for short-circuiting both surfaces of the ceramic member. All ofthe above-described oxygen separators can be used as oxidation reactors(for example, reactors for partial oxidation of hydrocarbons) or otherchemical reactors by supplying, for example, a hydrocarbon-containinggas into the oxidation reaction chamber.

The present invention will be described below in greater detail based onworking examples.

TEST EXAMPLE 1 Fabrication of Sintered Body (1)

La₂O₃, SrCO₃, TiO₂ and Fe₂O₃ as starting material powders were mixed soas to obtain stoichiometric ratios of x=0.1 and y=0.9 in the formula(La_(1-x)Sr_(x))(Ti_(1-y)Fe_(y))O₃ representing the composition of thesintered body obtained after firing. The mixture was prefired at atemperature of 1000° C. in air, and the obtained prefired material wasground and molded into a disk with a diameter of 22 mm and a thicknessof 1.5 mm. A sintered body of Test Example 1 was fabricated by firingthe molded body at a temperature of 1600° C. in air.

TEST EXAMPLE 2 to 4 Fabrication of Sintered Bodies (2)-(4)

La₂O₃, SrCO₃, TiO₂ and Fe₂O₃ as starting material powders were mixed soas to obtain stoichiometric ratios of x and y of 0.6 and 0.9,respectively (Test Example 2), 0.9 and 0.9 (Test Example 3), and 0.6 and0.5 (Test Example 4) in the aforesaid chemical formula. With respect toother conditions, the sintered bodies of Test Examples 2 to 4 werefabricated in the same manner as in Test Example 1.

TEST EXAMPLE 5 Fabrication of Sintered Body (5)

La₂O₃, CaCO₃, TiO₂ and Fe₂O₃ as starting material powders were mixed soas to obtain stoichiometric ratios of x=0.5 and y=0.9 in the formula(La_(1-x)Ca_(x))(Ti_(1-y)Fe_(y))O₃ representing the composition of thesintered body obtained after firing. With respect to other conditions,the sintered body of Test Example 5 was fabricated in the same manner asin Test Example 1.

TEST EXAMPLE 6 Fabrication of Sintered Body (6)

The sintered body of Test Example 6 was fabricated in the same manner asin Test Example 5, except that BaCO₃ was used as the starting materialinstead of CaCO₃.

TEST EXAMPLE 7 Evaluation of Electric Conductivity

The electric conductivity of the sintered bodies obtained in TestExample 1 was measured. The measurements were conducted using thefollowing method. That is, a sample in the form of a rectangularparallelepiped was cut out of each sintered body. A platinum pasteserving as an electrode was applied to those samples, then platinumwires were connected and firing was conducted at a temperature of850-1100° C. The specific conductance σ (S/cm²) was then determined bymeasuring the electric resistance of the samples in an apparatus inwhich the partial pressure of oxygen and temperature could be adjustedto any value. The relationship between the temperature and specificconductance σ obtained at a constant partial pressure of oxygen P_(O2)(approximately 0.1 Pa (approximately 10⁻⁶ atm)) is shown in Table 1, andthe relationship between the specific conductance σ and the partialpressure of oxygen P_(O2) at a constant temperature (800° C.) is shownin Table 2. TABLE 1 Temperature (° C.) log σ (S/cm²) 550 −0.7 600 −0.6650 −0.6 700 −0.5 750 −0.4 800 −0.3 850 −0.2 900 −0.2Partial pressure of oxygen PO₂ is approximately 0.1 Pa

TABLE 2 log P_(O2) (atm) log σ (S/cm²) 0.1 0.7 −0.7 0.5 −6.4 −0.3 −13.5−1.0 −14.2 −1.0 −17.1 −1.0 −22.0 −0.8 −26.0 −0.2Temperature 800° C.

As shown in Table 1 and Table 2, the sintered bodies obtained in TestExample 1 demonstrated good electron-conductive oxygen ion conductivityin a high-temperature range. This result indicates that the sinteredbodies of Test Example 1 can be used for causing the permeation ofoxygen ions, without short-circuiting the two surfaces of the sinteredbody, for example, with outer electrodes or outer circuits.

TEST EXAMPLE 8 Evaluation of Oxygen Separation Ability

Ceramic members for oxygen separation were fabricated by applying(La_(0.7)Sr_(0.3))CoO₃, as an oxygen ion permeation-enhancing catalystto both surfaces of each sintered body obtained in Test Examples 1thorough 6. Then, oxygen ion permeation modules 1 with the configurationshown in FIG. 1 were fabricated using those ceramic members. Air as theoxygen-containing gas (partial pressure of oxygen approximately 200 hPa(approximately 0.2 atm)) was supplied at a flow rate of 100 mL/min intothe oxygen source supply chamber 20 of the oxygen ion permeation module1. Further, nitrogen (partial pressure of oxygen approximately 0.1 Pa(approximately 10⁻⁵ atm)) as an oxidation reaction chamber gas wassupplied at a flow rate of 20 mL/min into the oxidation reaction chamber30. In this state, the temperature of the oxygen ion permeation module 1(ceramic material 10) was adjusted to 800° C. and maintained for 30 min.Then, the quantity of oxygen contained in the oxidation reaction chambergas released from the oxidation reaction chamber 30 was measured by gaschromatography, and the amount of oxygen (calculated as oxygenmolecules; μmol/min-cm²) that permeated through the ceramic member 10 ata temperature of 800° C. was evaluated. Similarly, the amounts of oxygenthat permeated at a temperature of 850° C. and 900° C. were evaluated.The results are shown in Table 3. TABLE 3 Ceramic Oxygen permeation ratecomposition (μmol/cm²-min) M x y 800° C. 850° C. 900° C. Working Example1 Sr 0.1 0.9 16 17 20 Working Example 2 Sr 0.6 0.9 24 25 25 WorkingExample 3 Sr 0.9 0.9 31 33 34 Working Example 4 Sr 0.6 0.5 22 24 24Working Example 5 Ca 0.5 0.9 25 27 26 Working Example 6 Ba 0.5 0.9 20 2019

As shown in Table 3, all the ceramic members using the sintered bodiesof Test Examples 1 through 6 have good oxygen permeability. This resultleads to the conclusion that those ceramic members have excellent oxygenseparation ability.

TEST EXAMPLE 9 Evaluation of Hydrocarbon Partial Oxidation Ability (1)

Ceramic members for partial oxidation of hydrocarbons were fabricated byapplying (La, Sr)CoO₃ as an oxygen ion permeation-enhancing catalyst tothe surface, on the side of the oxygen source supply chamber, of eachsintered body obtained in Test Examples 1 through 6, and applying anNi-containing catalyst serving as an oxidation-enhancing catalyst to thesurface on the side of the oxidation reaction chamber. The oxygen ionpermeation modules 1 with the configuration shown in FIG. 1 werefabricated in the same manner as in Test Example 8 using those ceramicmembers. Air as an oxygen-containing gas (partial pressure of oxygenapproximately 200 hPa (approximately 0.2 atm)) was supplied at a flowrate of 100 mL/min into the oxygen source supply chamber 20 of theoxygen ion permeation module 1. Further, a methane-nitrogen gas mixture(methane:nitrogen volume ratio was 1:1) as the oxidation reactionchamber gas was supplied at a flow rate of 5-20 mL/min into theoxidation reaction chamber 30. In this state, the temperature of theoxygen ion permeation module 1 (ceramic member 10) was adjusted to 900°C. and maintained for 30 min. Then, the quantity of CO and CO₂ containedin the oxidation reaction chamber gas discharged from the oxidationreaction chamber 30 was measured by gas chromatography, and the amountof oxygen (calculated as oxygen molecules; μmol/min-cm²) that permeatedthrough the ceramic member 10 at a temperature of 900° C. was evaluated.Practically no oxygen was contained in the gas discharged from theoxidation reaction chamber. Similarly, the amount of oxygen thatpermeated at a temperature of 1000° C. was evaluated. The results areshown in Table 4. TABLE 4 Oxygen Ceramic permeation rate composition(μmol/cm²-min) M x y 900° C. 1000° C. Working Example 1 Sr 0.1 0.9 24125 Working Example 2 Sr 0.6 0.9 52 54 Working Example 3 Sr 0.9 0.9 5553 Working Example 4 Sr 0.6 0.5 45 52 Working Example 5 Ca 0.5 0.9 54 55Working Example 6 Ba 0.5 0.9 43 45

As shown in Table 4, all the ceramic members using the sintered bodiesof Test Examples 1 through 6 had good oxygen permeability calculatedfrom the amount of CO and CO₂. This result leads to the conclusion thatthose ceramic members have excellent partial oxidation ability withrespect to methane (partial oxidation ability with respect tohydrocarbons).

TEST EXAMPLE 10 Fabrication of Sintered Body (7)

La₂O₃, SrCO₃, TiO₂ and Fe₂O₃ as starting material powders were mixed soas to obtain stoichiometric ratios of x=0.4 and y=0.9 in the formula(La_(1-x)Sr_(x))(Ti_(1-y)Fe_(y))O₃ representing the composition of thesintered body obtained after firing. The mixture was prefired at atemperature of 1000° C. in air, and the obtained prefired material wasground and molded into a disk with a diameter of 22 mm and a thicknessof 1.5 mm. A sintered body (ceramic) of Test Example 10 was fabricatedby firing the molded body at a temperature of 1600° C. in air.

TEST EXAMPLE 11 Fabrication of Sintered Body (8)

La₂O₃, BaCO₃, TiO₂ and Fe₂O₃ as starting material powders were mixed soas to obtain stoichiometric ratios (almost the same composition as thatof Test Example 6) of x=0.5 and y=0.9 in the formula(La_(1-x)Ba_(x))(Ti_(1-y)Fe_(y))O₃ representing the composition of thesintered body obtained after firing. With respect to other conditions,the sintered body of Test Example 11 was fabricated in the same manneras in Test Example 10.

TEST EXAMPLE 12 Fabrication of Sintered Body (9)

La₂O₃, CaCO₃, TiO₂ and Fe₂O₃ as starting material powders were mixed soas to obtain stoichiometric ratios of x=0.35 and y=0.9 in the formula(La_(1-x)Ca_(x))(T_(1-y)Fe_(y))O₃ representing the composition of thesintered body obtained after firing. With respect to other conditions,the sintered body of Test Example 12 was fabricated in the same manneras in Test Example 10.

TEST EXAMPLE 13 Fabrication of Comparative Sintered Body

La₂O₃, SrCO₃, Ga₂O₃ and Fe₂O₃ as starting material powders were mixed soas to obtain stoichiometric ratios of x=0.3 and y=0.4 in the formula(La_(1-x)Sr_(x))(Ga_(1-y)Fe_(y))O₃ representing the composition of thesintered body obtained after firing. With respect to other conditions,the sintered body (comparative sintered body) of Test Example 13 wasfabricated in the same manner as in Test Example 10.

TEST EXAMPLE 14 Evaluation of Hydrocarbon Partial Oxidation Ability (2)

Ceramic members for partial oxidation of hydrocarbons were fabricated byapplying (La, Sr)CoO₃ as an oxygen ion permeation-enhancing catalyst tothe surface, on the side of the oxygen source supply chamber, of eachsintered body obtained in Test Examples 10 through 13, and applying anNi-containing catalyst serving as an oxidation-enhancing catalyst to thesurface on the side of the oxidation reaction chamber. The oxygen ionpermeation modules 1 with the configuration shown in FIG. 1 wereproduced using these ceramic members. Air as an oxygen-containing gas(partial pressure of oxygen approximately 200 hPa (approximately 0.2atm)) was supplied at a flow rate of 500 mL/min into the oxygen sourcesupply chamber 20 of the oxygen ion permeation module 1. Further, amethane-nitrogen gas mixture (methane:nitrogen volume ratio was 55:45)as an oxidation reaction chamber gas was supplied at a flow rate of 15mL/min into the oxidation reaction chamber. The oxygen supply flow ratewas approximately 12 times that of hydrocarbon (here, methane). In thisstate, the temperature of the oxygen ion permeation module 1 (ceramicmember 10) was adjusted to 900° C. and maintained for 30 min. Then, thecomposition of the oxidation reaction chamber gas discharged from theoxidation reaction chamber 30 was measured by gas chromatography, andthe amount of oxygen (calculated as oxygen molecules; μmol/min-cm²) thatpermeated through the ceramic member 10 at a temperature of 900° C. wasevaluated from the amounts of chemical species (here, substantially CO,CO₂, and O₂) containing oxygen. The results are shown in Table 5. TABLE5 Composition of gas released from oxidation reaction Oxygen chamber(vol. %) permeation rate Ceramic composition H₂ CO CH₄ CO₂ O₂(μmol/cm²-min) Working La_(0.6)Sr_(0.4)Ti_(0.1)Fe_(0.9)O₃ 28 14 16 3 0.2125 Example 10 Working La_(0.5)Ba_(0.5)Ti_(0.1)Fe_(0.9)O₃ 29 13 14 1 0.398 Example 11 Working La_(0.65)Ca_(0.35)Ti_(0.1)Fe_(0.9)O₃ 38 10 12 10.2 73 Example 12 Working La_(0.7)Sr_(0.3)Ga_(0.6)Fe_(0.4)O₃ 37 16 130.8 0.25 100 Example 13

As shown in Table 5, all the ceramic members using the sintered bodiesof Test Examples 10 through 12 had good oxygen permeability calculatedfrom the amount of CO, CO₂ and O₂. This result leads to the conclusionthat those ceramic members have excellent partial oxidation ability withrespect to methane (partial oxidation ability with respect tohydrocarbons). This oxygen permeability is similar to that of theceramic member using a sintered body (comparative sintered body) of TestExample 13, which was represented by the chemical formula(La_(0.7)Sr_(0.3))(Ga_(0.8)Fe_(0.4))O₃, or superior to the ceramicmember of Test Example 13. Furthermore, TiO₂ used as the startingmaterial powder for the sintered bodies of Test Examples 10 to 12obviously could be acquired at a lower cost than Ga₂O₃ used as thestarting material powder for the sintered body of Test Example 13.Moreover, visual observation of the surface of each ceramic member onthe side of the oxidation reaction chamber after the evaluation testsdemonstrated that the precipitation of carbon in the case of ceramicmembers of Test Examples 10 to 12 is less than that for the ceramicmember of Test Example 4. No abnormal cracking was observed in any ofthe ceramic members after the evaluation tests.

TEST EXAMPLE 15 Fabrication of Sintered Body (10)

La₂O₃, SrCO₃, TiO₂ and Fe₂O₃ as starting material powders were mixed soas to obtain stoichiometric ratios of x=0.3 and y=0.9 in the formula(La_(1-x)Sr_(x))(Ti_(1-y)Fe_(y))O₃ representing the composition of thesintered body obtained after firing. The mixture was prefired at atemperature of 1000° C. in air, and the obtained prefired material wasground and molded into a test tube (closed-end tube with round bottom)with an outer diameter of 20 mm and a length of 150 mm. A sintered body(ceramic) of Test Example 15 was fabricated by firing the molded body ata temperature of 1600° C. in air. The membrane thickness (thickness ofthe wall) of the sintered body thus obtained was approximately 0.5 mm.

TEST EXAMPLE 16 Fabrication of Sintered Body (11)

La₂O₃, SrCO₃, TiO₂ and Fe₂O₃ as starting material powders were mixed soas to obtain stoichiometric ratios of x=0.3 and y=0.7 in the aforesaidchemical formula. With respect to other conditions, the sintered body ofTest Example 16 was fabricated in the same manner as in Test Example 15.The membrane thickness of the sintered body thus obtained was 0.3 mm orless (approximately 0.28 mm).

TEST EXAMPLE 17 Fabrication of Sintered Body (12)

La₂O₃, SrCO₃, TiO₂ and Fe₂O₃ as starting material powders were mixed soas to obtain stoichiometric ratios of x=0.5 and y=0.5 in the aforesaidchemical formula. With respect to other conditions, the sintered body ofTest Example 17 was fabricated in the same manner as in Test Example 15.The membrane thickness of the sintered body thus obtained was 0.3 mm orless (approximately 0.28 mm).

TEST EXAMPLE 18 Fabrication of Sintered Body (13)

La₂O₃, SrCO₃, TiO₂ and Fe₂O₃ as starting material powders were mixed soas to obtain stoichiometric ratios of x=0.7 and y=0.5 in the aforesaidchemical formula. With respect to other conditions, the sintered body ofTest Example 18 was fabricated in the same manner as in Test Example 15.The membrane thickness of the sintered body thus obtained wasapproximately 0.3 mm.

TEST EXAMPLE 19 Fabrication of Sintered Body (14)

La₂O₃, BaCO₃, TiO₂ and Fe₂O₃ as starting material powders were mixed soas to obtain stoichiometric ratios of x=0.4 and y=0.8 in the formula(La_(1-x)Ba_(x))(Ti_(1-y)Fe_(y))O₃ representing the composition of thesintered body obtained after firing. With respect to other conditions,the sintered body of Test Example 19 was fabricated in the same manneras in Test Example 15. The membrane thickness of the sintered body thusobtained was approximately 0.6 mm.

TEST EXAMPLE 20 Fabrication of Sintered Body (15)

La₂O₃, BaCO₃, TiO₂ and Fe₂O₃ as starting material powders were mixed soas to obtain stoichiometric ratios of x=0.4 and y=0.6 in the aforesaidchemical formula. With respect to other conditions, the sintered body ofTest Example 20 was fabricated in the same manner as in Test Example 19.The membrane thickness of the sintered body thus obtained wasapproximately 0.4 mm or less (approximately 0.36 mm).

TEST EXAMPLE 21 Fabrication of Sintered Body (16)

La₂O₃, CaCO₃, TiO₂ and Fe₂O₃ as starting material powders were mixed soas to obtain stoichiometric ratios of x=0.25 and y=0.75 in the formula(La_(1-x)Ca_(x))(Ti_(1-y)Fe_(y))O₃ representing the composition of thesintered body obtained after firing. With respect to other conditions,the sintered body of Test Example 21 was fabricated in the same manneras in Test Example 15. The membrane thickness of the sintered body thusobtained was approximately 0.5 mm or less (approximately 0.48 mm).

TEST EXAMPLE 22 Evaluation of Hydrocarbon Partial Oxidation Ability (3)

(La, Sr)CoO₃ as an oxygen ion permeation-enhancing catalyst was causedto adhere to the inner surface (surface on the side of the oxygen sourcesupply chamber) of each sintered body obtained in Test Examples 15through 21. Then, an Ni-containing catalyst serving as theoxidation-enhancing catalyst was caused to adhere to the outer surface(surface on the side of the oxidation reaction chamber) of thosesintered bodies. Ceramic members for partial oxidation of hydrocarbonswere thus fabricated. The oxygen ion permeation modules 1 with theconfiguration shown in FIG. 7 were fabricated using these ceramicmembers. Air as an oxygen-containing gas (partial pressure of oxygenapproximately 200 hPa (approximately 0.2 atm)) was supplied at a flowrate of 1000 mL/min into the oxygen source supply chamber 20 of theoxygen ion permeation module 1. Further, a methane-nitrogen gas mixture(methane:nitrogen volume ratio was 2:1) as the oxidation reactionchamber gas was supplied at a flow rate of 5-60 mL/min (here 15 mL/min)into the oxidation reaction chamber 30. In this state, the temperatureof the oxygen ion permeation module 1 (ceramic member 10) was adjustedto 900° C. and maintained for 30 min. Then, the composition of theoxidation reaction chamber gas discharged from the oxidation reactionchamber 30 was measured by gas chromatography, and the amount of oxygen(calculated as oxygen molecules; μmol/min-cm²) that permeated throughthe ceramic member 10 at a temperature of 900° C. was evaluated from theamounts of chemical species (here, substantially CO, CO₂, and O₂)containing oxygen. The results are shown in Table 6. TABLE 6 Oxygenperme- ation Reduc- Film rate tion ex- thick- (μmol/ pansion En- nesscm²- ratio dur- (μm) min) (%) ance WorkingLa_(0.7)Sr_(0.3)Ti_(0.1)Fe_(0.9)O₃ 0.5 125 0.7 ◯ Example 15 WorkingLa_(0.7)Sr_(0.3)Ti_(0.3)Fe_(0.7)O₃ <0.3 35 0.1

Example 16 Working La_(0.5)Sr_(0.5)Ti_(0.5)Fe_(0.5)O₃ <0.3 12 <0.01

Example 17 Working La_(0.3)Sr_(0.7)Ti_(0.5)Fe_(0.5)O₃ 0.3 29 0.3 ◯Example 18 Working La_(0.6)Ba_(0.4)Ti_(0.4)Fe_(0.8)O₃ 0.6 98 0.65 ◯Example 19 Working La_(0.6)Ba_(0.4)Ti_(0.2)Fe_(0.6)O₃ <0.4 23 0.1

Example 20 Working La_(0.75)Ca_(0.25)Ti_(0.25)Fe_(0.75)O₃ <0.5 20 0.1

Example 21

As shown in Table 6, all the ceramic members using the sintered bodiesof Test Examples 15 through 21 had good oxygen permeability calculatedfrom the amount of CO and CO₂. This result leads to the conclusion thatthese ceramic members have excellent partial oxidation ability withrespect to methane (partial oxidation ability with respect tohydrocarbons).

TEST EXAMPLE 23 Evaluation of Thermal Expansion Coefficient

Sintered bodies were fabricated in the same manner as in Test Examples15 through 21, except that the prefired material was molded into acylindrical columnar shape. Samples with the cylindrical columnar shapehaving a diameter of 5 mm and a length of 20 mm were fabricated bycutting those sintered bodies. An elongation within a temperature rangefrom room temperature to 800° C. was measured in the air atmosphere(partial pressure of oxygen is approximately 200 hPa (approximately 0.2atm)), and a reducing atmosphere (contains hydrogen 5 vol. % andnitrogen 95 vol. %) by using the samples and this elongation wasrepresented as a percentage of the length at room temperature. Thermalexpansion coefficient E_(air) in the air atmosphere, and thermalexpansion coefficient E_(red) in the reducing atmosphere, were thusfound for each sintered body. The difference therebetween(E_(red)−E_(air)) is represented in Table 6 as a reduction expansionratio (%) of each sintered body.

TEST EXAMPLE 24 Evaluation of Endurance

A hydrocarbon partial oxidation test was continuously conducted underthe same conditions as in Test Example 22 and the composition of theoxidation reaction chamber gas that was discharged was measured by gaschromatography. As a result, the interval from the start of the test tothe initiation of cracking in the sintered bodies (until air starts toleak) was investigated. The results are also presented in Table 6. Thereference symbol “{circumflex over (×)}” in the table relates to thecases in which the interval from the test start to the occurrence ofleak was 10 h or more, and the reference symbol “◯” relates to the casesin which the interval to the leak occurrence was 2 h or more (2 to 10h). A sintered body having the composition((La_(0.7)Sr_(0.3))(Ga_(0.6)Fe_(0.4))O₃) of Test Example 13 wasfabricated by operations identical to those of Test Example 15, and theendurance of the sintered bodies was evaluated by conducting ahydrocarbon partial oxidation test in the same manner as that used forthe sintered bodies in Test Examples 15 through 21. Leaks started withinless than 1 h from the start of the test.

Specific examples of the present invention were described above.However, those examples are merely illustrative and place no limitationon the claims. The technology described in the patent claims includesmodifications and changes of the above-described illustrative examples.Further, the technological features explained in the presentspecification or appended drawings demonstrate technological utilitywhen used individually or in a variety of combinations and are notlimited to the combinations described at the time of filing. Moreover,the technology illustrated in the present specification or appendeddrawings achieves a plurality of objects at the same time, and achievingeven one object among them possesses by itself a technological utility.

1. A ceramic member having a perovskite-type crystal structure and acomposition represented by the general formula:(Ln_(1-x)M_(x))(Ti_(1-y)Fe_(y))O₃ (where Ln represents at least oneelement selected from lanthanoids; M represents at least one elementselected from the group containing Sr, Ca, and Ba; and 0<x<1, 0.4≦y<1,x+y≧1).
 2. A ceramic member according to claim 1, wherein said M is Sr;said x satisfies the condition 0.3≦x≦0.5; and said y satisfies thecondition 0.85≦y<1.
 3. A ceramic member according to claim 1, whereinsaid M is Ba; said x satisfies the condition 0.4≦x≦0.6; and said ysatisfies the condition 0.85≦y<1.
 4. A ceramic member according to claim1, wherein said M is Ca; said x satisfies the condition 0.25≦x≦0.45; andsaid y satisfies the condition 0.85≦y<1.
 5. A ceramic member accordingto claim 1, wherein said M is Sr; said x satisfies the condition0.2≦x≦0.6; said y satisfies the condition 0.5≦y<1; and said x+ysatisfies the condition 1≦x+y<1.2.
 6. A ceramic member according toclaim 1, wherein
 10. (Cancelled)
 11. A laminated oxygen ion conductivepart comprising: a porous support body; and at least one membranousceramic member with a thickness of 0.5 mm or less which is provided onthe surface of the porous support body, said ceramic member having aperovskite-type crystal structure represented by any of the following(A)-(C): (A) the general formula(Ln_(1-x)Sr_(x))(Ti_(1-y)Fe_(y))O₃ where said Ln represents at least oneelement selected from lanthanoids, said x satisfies the condition0.2≦x≦0.6, said y satisfies the condition 0.5≦y<1, and x and y satisfythe condition 1≦x+y<1.2; (B) the general formula(Ln_(1-x)Ba_(x))(Ti_(1-y)Fe_(y))O₃ where said Ln represents at least oneelement selected from lanthanoids, said x satisfies the condition0.3≦x≦0.7, said y satisfies the condition 0.5≦y<1, and x and y satisfythe condition 1≦x+y<1.2; and (C) the general formula(Ln_(1-x)Ca_(x))(Ti_(1-y)Fe_(y))O₃ where said Ln represents at least oneelement selected from lanthanoids, said x satisfies the condition0.2≦x≦0.55, said y satisfies the condition 0.5≦y<1, and x and y satisfythe condition 1≦x+y<1.2 .
 12. A laminated oxygen ion conductive partaccording to claim 11, wherein a catalyst for enhancing the permeationof oxygen ions is applied to the surface of the aforesaid membranousceramic material and/or the aforesaid porous support body.
 13. Alaminated oxygen ion conductive part according to claim 12, comprising(La_(x)Sr_(1-x))M′O₃ (where, 0.1≦x<1, and M′ is at least one selectedfrom Co, Cu, Fe, and Mn) as the aforesaid catalyst for enhancing thepermeation of oxygen ions.
 14. An oxygen ion permeation modulecomprising: a casing; at least one membranous ceramic member with oxygenion conductivity and a thickness of 0.5 mm or less which is accommodatedin the casing, said ceramic member having a perovskite-type crystalstructure represented by any of the following (A)-(C): (A) the generalformula(Ln_(1-x)Sr_(x))(Ti_(1-y)Fe_(y))O₃ where said Ln represents at least oneelement selected from lanthanoids, said x satisfies the condition0.2≦x≦0.6, said y satisfies the condition 0.5≦y<1, and x and y satisfythe condition 1≦x+y<1.2; (B) the general formula(Ln_(1-x)Ba_(x))(Ti_(1-y)Fe_(y))O₃ where said Ln represents at least oneelement selected from lanthanoids, said x satisfies the condition0.3≦x≦0.7, said y satisfies the condition 0.5≦y<1, and x and y satisfythe condition 1≦x+y<1.2; and (C) the general formula(Ln_(1-x)Ca_(x))(Ti_(1-y)Fe_(y))O₃ where said Ln represents at least oneelement selected from lanthanoids, said x satisfies the condition0.2≦x≦0.55, said y satisfies the condition 0.5≦y<1, and x and y satisfythe condition 1≦x+y<1.2; an oxygen source supply chamber for supplyingan oxygen-containing gas from the outside, this chamber being providedinside the casing so as to face the ceramic member; and an oxidationreaction chamber provided inside the casing so as to face the ceramicmember, hermetically separated from the oxygen source supply chamber viathe ceramic member and serving to induce an oxidation reaction with theparticipation of oxygen ions that are supplied by permeation through theceramic member from said oxygen source supply chamber.
 15. An oxygen ionpermeation module according to claim 14, wherein a catalyst forenhancing the permeation of oxygen ions is applied to the surface of theaforesaid membranous ceramic member on the side of the oxygen sourcesupply chamber.
 16. An oxygen ion permeation module according to claim15, comprising (La_(x)Sr_(1-x))M′O₃ (where, 0.1≦x<1, and M′ is at leastone selected from Co, Cu, Fe, and Mn) as said catalyst for enhancing thepermeation of oxygen ions.
 17. An oxygen ion permeation module accordingto claim 14, wherein a catalyst for enhancing the oxidation reaction isapplied to the surface of the aforesaid membranous ceramic member on theside of the oxidation reaction chamber.
 18. An oxygen ion permeationmodule according to claim 17, comprising an Ni-based catalyst as theaforesaid catalyst for enhancing the oxidation reaction.
 19. An oxygenion permeation module comprising: a casing; a laminated oxygen ionconductive part according to claim 11, which is accommodated in thecasing; an oxygen source supply chamber for supplying anoxygen-containing gas from the outside, this chamber being providedinside the casing so as to face the laminated oxygen ion conductivepart; and an oxidation reaction chamber provided inside the casing so asto face the laminated oxygen ion conductive part, hermetically separatedfrom the oxygen source supply chamber via this part and serving toinduce an oxidation reaction with the participation of oxygen ions thatare supplied by permeation through the ceramic member from said oxygensource supply chamber.
 20. An oxygen ion permeation module according toclaim 19, wherein a catalyst for enhancing the permeation of oxygen ionsis applied to the surface of the aforesaid ceramic member on the side ofthe oxygen source supply chamber and/or the aforesaid porous supportbody located on the side of the oxygen source supply chamber from theaforesaid ceramic member.
 21. An oxygen ion permeation module accordingto claim 20, comprising (La_(x)Sr_(1-x))M′O₃ (where 0.1≦x<1, and M′ isat least one selected from Co, Cu, Fe, and Mn) as the aforesaid catalystfor enhancing the permeation of oxygen ions.
 22. An oxygen ionpermeation module according to claim 19, wherein a catalyst forenhancing the oxidation reaction is applied to the surface of theaforesaid ceramic member on the side of the oxidation reaction chamberand/or the aforesaid porous support body located on the side of theoxidation reaction chamber from the aforesaid ceramic member.
 23. Anoxygen ion permeation module according to claim 22, comprising anNi-based catalyst as the aforesaid catalyst for enhancing the oxidationreaction.
 24. An oxygen separator comprising: an oxygen ion permeationmodule according to claim 14; an oxygen source supply means for causinga gas containing oxygen to flow through to the oxygen source supplychamber of the module and bringing the gas into contact with the surfaceof the aforesaid ceramic member on the side of the oxygen source supplychamber; and an oxidation reaction chamber gas circulation means forcausing a gas with a partial pressure of oxygen lower than that on theoxygen source supply chamber side to flow through to the oxidationreaction chamber of the module and bringing the gas into contact withthe surface of the ceramic member on the side of the oxidation reactionchamber.
 25. An oxygen separator comprising: an oxygen ion permeationmodule according to claim 19; an oxygen source supply means for causinga gas containing oxygen to flow through to the oxygen source supplychamber of the module and bringing the gas into contact with the surfaceof the ceramic member on the side of the oxygen source supply chamber;and an oxidation reaction chamber gas circulation means for causing agas with a partial pressure of oxygen lower than that on the oxygensource supply chamber side to flow through to the oxidation reactionchamber of the module and bringing the gas into contact with the surfaceof the ceramic member on the side of the oxidation reaction chamber. 26.An oxidation reactor comprising: an oxygen ion permeation moduleaccording to claim 14; an oxygen source supply means for supplying a gascontaining oxygen to the oxygen source supply chamber of the module andbringing the gas into contact with the surface of the aforesaid ceramicmember on the side of the oxygen source supply chamber; and an oxidationtarget gas supply means for supplying a gas containing the oxidationtarget gas and having a partial pressure of oxygen lower than that onthe oxygen source supply chamber side to the oxidation reaction chamberof the module and bringing the gas into contact with the surface of theceramic member on the side of the oxidation reaction chamber.
 27. Areactor for partial oxidation of hydrocarbons, which is the oxidationreactor of claim 26, wherein the aforesaid oxidation target gas is ahydrocarbon, and the flow rate of oxygen supplied by the aforesaidoxygen source supply means is by a factor of two or more higher than theflow rate of the hydrocarbon supplied by the aforesaid oxidation targetgas supply means.
 28. An oxidation reactor comprising: An oxygen ionpermeation module according to claim 19; an oxygen source supply meansfor supplying a gas containing oxygen to the oxygen source supplychamber of the module and bringing the gas into contact with the surfaceof the aforesaid ceramic member on the side of the oxygen source supplychamber; and an oxidation target gas supply means for supplying a gascontaining the oxidation target gas and having a partial pressure ofoxygen lower than that on the oxygen source supply chamber side to theoxidation reaction chamber of the module and bringing the gas intocontact with the surface of the ceramic member on the side of theoxidation reaction chamber.
 29. A reactor for partial oxidation ofhydrocarbons, which is the oxidation reactor of claim 28, wherein theaforesaid oxidation target gas is a hydrocarbon, and the flow rate ofoxygen supplied by the aforesaid oxygen source supply means is by afactor of two or more higher than the flow rate of the hydrocarbonsupplied by the aforesaid oxidation target gas supply means.